AtLanta — Nearly half of all American workers do not have paid sick leave, and half of these are more likely to go to work feeling unwell – or send an ill child to school – rather than take an unpaid day off.

These findings threaten to undermine President Obama's effort to have anyone exhibiting swine-flu-like symptoms stay at home for as many as four days. The emphasis on prevention and individual responsibility is a welcome departure from the punitive government actions – such as quarantines and forced vaccinations – called for under previous pandemic-response plans, some health experts say.

But for the 48 percent of Americans without paid sick leave, the policy presents a choice between two equally undesirable options: stay at home and lose money or go to work despite government exhortations not to. Businesses, too, say the situation leads to so-called "presenteeism," or the act of going to work while unwell, costing the economy $180 million a year, by one estimate.

The swine flu outbreak "ties back to the issue of employment rights and social support," says Marc Rodwin, author of "Medicine, Money and Morals." "There's a conflict between what's good for the public and what's good for the individual."

An estimated 100 million workers stand to lose pay if they follow Mr. Obama's advice and stay home. Some 60 million of these Americans – 48 percent of all US workers – have no sick leave at all, according to the independent Institute for Women's Policy Research, in Washington. (The US Labor Department put the figure at 43 percent in 2007.) Others lack flextime that would let them to stay home to care for family members. These data have helped to create momentum to reform labor laws. So have events on the ground.

Though the Obama administration has urged schools to stay open, 351 were closed in the third week of October because of swine flu. Some 600 have closed temporarily this school year, according to the Associated Press.

When schools close, at least one parent often needs to stay home with a child. If the US were to close all its schools for a month, the cost to the US economy would be $10 billion to $47 billion, according to a Brookings Institution study.

Businesses see a different problem – workers showing up when perhaps they should have stayed home. Presenteeism is a major problem, said 56 percent of human resources managers in a recent survey. Employees who come to work unwell tend to have lower productivity and may pass the virus to other workers, they say. The $180 billion hit the economy takes every year from presenteeism surpasses the costs of absenteeism, estimates the National Partnership for Women and Families in Washington.

The burdens of these measures tend to fall hardest on low-income Americans, especially those in service industries such as restaurants and nursing care, and mall workers, where the share of workers without paid leave is relatively high.

"The flu epidemic really brings into sharp relief the kind of strain that this is putting on families," says Debra Ness, president of the National Partnership for Women and Families. "Our public officials are saying to people, 'If you feel sick, stay at home.' For millions of people, this is advice that's not simple to follow."

The Kaiser Family Foundation reported last year that half of workers with no paid sick leave chose to work when they were feeling unwell, rather than stay home.

So far, cities and states are taking the lead on confronting the issue.

Legislation in Maine would require large employers to give workers six paid sick days a year. Firms with fewer than 25 workers would give an hour of sick leave for every 80 hours worked. The law would apply to both full- and part-time workers.

"We are all being advised by our doctors to stay home if we're sick, but that is a cruel piece of advice if you don't have paid sick time," Maine Senate President Elizabeth Mitchell said recently.

The backdrop to the debate is the shift Obama has made in pandemic planning. By leaving decisions to the individual and focusing on prevention, he has won plaudits for approaching the pandemic with a balance of concern and context, says Mr. Rodwin, also a law professor at Suffolk University in Boston.

But businesses are pushing back. They say many firms can't afford to subsidize the government's strategy – especially if mandatory sick-leave laws are passed.

"Government is trying to do something that's well intentioned, but they have no idea what the effect is on a small-business owner," Jack Friedman of the Queens Chamber of Commerce in New York City told CNN last month.

"The difference between what we're offering and what the government is requiring us to offer could cost our business tens of thousands of dollars."